Fix feedback prompt on dark mode

Summary:
https://pxl.cl/2tKXq

It was reported the feedback prompt title was unreadable.

Reviewed By: mweststrate

Differential Revision: D43533800

fbshipit-source-id: f756a9822c479105dae890159518c05c99405fb7

desktop/flipper-ui-core/src/chrome/RatingButton.tsx

@@ -30,7 +30,7 @@ import {StarOutlined} from '@ant-design/icons';
 import {Popover, Rate} from 'antd';
 import {useStore} from '../utils/useStore';
 import {isLoggedIn} from '../fb-stubs/user';
-import {useValue} from 'flipper-plugin';
+import {theme, useValue} from 'flipper-plugin';
 import {reportPlatformFailures} from 'flipper-common';
 import {getRenderHostInstance} from 'flipper-frontend-core';
 
@@ -254,7 +254,7 @@ class FeedbackComponent extends Component<
           paddingTop: 10,
           paddingBottom: 10,
         }}>
-        <Row key="heading" style={{color: 'black', fontSize: 20}}>
+        <Row key="heading" style={{color: theme.primaryColor, fontSize: 20}}>
           {this.state.nextAction === 'finished'
             ? this.props.promptData.postSubmitHeading
             : this.props.promptData.preSubmitHeading}